Separator plate unit with inclined separating wall having at least one metering point and fuel cell having separator plate unit thereof

ABSTRACT

The invention relates to a fuel cell having a membrane electrode arrangement ( 16 ) arranged between two separator plate units ( 44 ), a first fluid area ( 12 ) for distribution of a first fluid which is adjacent to one side of the membrane-electrode arrangement ( 16 ), a second fluid area ( 14 ) for distribution of a second fluid which is adjacent to a side of the membrane-electrode arrangement ( 16 ) opposite this side, with a separating wall ( 36 ) being arranged in at least one fluid area ( 12 ) and subdividing the fluid area ( 12 ) into at least one metering area ( 32 ) and one fluid subarea ( 34 ), with the at least one metering area ( 32 ) having a fluid connection to the adjacent fluid subarea ( 34 ) at at least one metering point ( 38 ), such that the first fluid can be metered from the metering area ( 32 ) through the metering point ( 38 ) into the adjacent fluid subarea ( 34 ). According to the invention, starting from an input point ( 24 ), at the edge, for the first fluid into the fluid area ( 12 ), a cross section of the fluid subarea ( 34 ) increases in the flow direction ( 40 ) of the first fluid towards an output port ( 26 ).

The invention relates to a fuel cell with a separator plate unit, and toa separator plate unit, as claimed in the precharacterizing clauses ofthe independent claims.

The basic design of a polymer electrolyte membrane fuel cell (PEM fuelcell) is known. The PEM fuel cell contains a membrane electrode assembly(MEA) which is formed from an anode, a cathode and a polymer electrolytemembrane (PEM) arranged between them. The MEA itself is in turn arrangedbetween two separator plate units, wherein a separator plate unit whichis arranged above the anode has channels for the distribution of fuel,for example hydrogen gas, a hydrogen-rich reformat gas or the like, anda separator plate unit which is arranged above the cathode has channelsfor the distribution of oxidant, for example air, wherein these channelsface the MEA. In the following text, channels such as these are alsoreferred to as distribution channels. The distribution channels form theso-called anode area and cathode area. The electrodes, the anode and thecathode, are in general in the form of so-called gas diffusionelectrodes (GDE). These have the function of carrying away the electriccurrent which is produced in the electrochemical fuel-cell reaction (forexample 2 H₂+O₂→2 H₂O) and of allowing the reaction substances (in theend hydrogen and oxygen), educts and products, to diffuse through. Ingeneral, a GDE comprises at least one gas diffusion layer (GDL) and acatalyst layer, which faces the PEM and on which the fuel cell reactiontakes place.

A fuel cell such as this can produce electric current with high power atrelatively low operating temperatures. Actual fuel cells are generallystacked to form so-called fuel cell stacks, in order to achieve a highpower outlet, in which case bipolar separator plates (bipolar plates)are used instead of the monopolar separator plates, and monopolarseparator plates are used only as end plates for the stack. Theseparator plates may comprise two or more plate elements which form aunit and for this reason are referred to as separator plate units. Inthe following text, the expression separator plate unit is intended tomean all the above-mentioned plates and plate units. A separator plateunit can accordingly comprise a single plate or may be assembled fromtwo or more plate elements, for example an anode plate and a cathodeplate.

Certain conventional PEMs require a certain water content in order tohave adequate ion conductivity. This relates in particular to PEMs whichare composed of materials based on fluorinated sulfonic acids, forexample Nafion. PEMs such as these are therefore generally moisturizedby moisturizing the reaction substances before they are supplied to aPEM fuel cell. The disadvantage of moisturizing is the complexityassociated with this and the devices which are additionally required,such as a moisturizer, which complicates the operating process and isnot consistent with a fuel cell system being of a type that is ascompact as possible.

A further disadvantage of moisturizing is that it is difficult to adjusta moisturization level. This is because, if moisturization is carriedout to an inadequate extent or not at all and it is assumed that theproduct water created during the fuel cell reaction is sufficient tomoisturize the PEM adequately, then this results, in particular on thecathode side, in the problem that there is a tendency to vaporizationfor water in the vicinity of the oxidant inlet port, because the oxidantis relatively dry there, as a result of which the PEM has a tendency todry out, particularly in this area. If it dries out, not only can theion conductivity then be lost, but the PEM can also be mechanicallydamaged, for example by cracks.

When flowing through the channels of the separator plate unit, theoxidant then absorbs product water from the MEA, as a result of whichits relative humidity increases and the moisturization problem isincreasingly reduced until, in the end, it disappears or, in poorcircumstances, even changes over to the opposite problem, a problem oftransporting water away.

The problem of transporting water away consists in that the oxidantbecomes increasingly more moist as it travels further from the inletport to the outlet port, as a result of product water absorption, andcan thus absorb, and hence transport away, ever less product water, suchthat it is even possible for a situation to arise at the outlet port orin its vicinity in which the product water is not adequately carriedaway. In poor circumstances, the product water then condenses and, forexample, blocks important paths for transporting the reaction substancesin and out to and from the reactive centers, thus adversely affectingthe fuel cell reaction, with the power of the fuel cell falling.

The problem of transporting water away can occur in particular when theoxidant is moisturized before entering a fuel cell. Although themoisturizing process means that the MEA is then sufficiently moist inthe area of the oxidant inlet port, in order to prevent the PEM fromdrying out, the oxidant can then, however, absorb less product waterfrom the start, as a result of which the moisture in the oxidant rapidlybecomes too high in order to adequately absorb and carry away productwater. The fuel cell reaction can therefore easily be adverselyaffected.

Thus, in general, a compromise between adequate moisturizing at thecathode inlet and adequate transportation of water away from the cathodeoutlet must therefore be found for conventional fuel cells withmoisture-dependent PEMs.

In order to solve the moisturizing problem, DE 103 46 594 A1 describes afuel cell which has two fluid areas, that is to say an anode area and acathode area, in which, in one of the fluid areas, a further fluid areais separated by a separating wall and is intended to be used as ametering area for a fluid, for example oxidant. The separating wall hasholes through which the metering area is fluidically connected to thecathode area, so that a fluid (the oxidant) flowing in the metering areacan enter the cathode area through holes which form the metering points,and can thus be injected or metered into the cathode area. The meteringarea allows the supply of oxidant to the cathode area to be spatiallydistributed over a larger area and thus spread out. In consequence,rather than the entire volume of the oxidant that is required for thefuel cell reaction flowing via that part of the PEM which isparticularly susceptible to drying out in the region of the inlet areaof the cathode, the amount in the optimum case is only so much as can beelectrochemically converted in this area. Since, initially, only a smallamount of oxidant is metered, only a small amount of water is alsorequired to moisturize the PEM, to be precise, in the optimum case, lessthan is created in this area as a result of the fuel cell reaction.Downstream, before a further metering point, the oxidant is then alreadypartially moisturized as a consequence of the water created in the fuelcell reaction, so that the metering of dry oxidant is even less damagingthan in the case of the previous metering. This trend continues furtherduring the subsequent metering processes as a result of which, overall,scarcely any or even no moisturized oxidant can be used for the fuelcell without its PEM or its function suffering damage as a result ofdrying out. Thus, in the optimum case, it may even be possible todispense with the moisturizing and water-recovery devices which havebeen required until now for PEM fuel cell systems, thus representing aconsiderable simplification of such PEM fuel cell systems.

Thus, although DE 103 46 594 A1 indicates a fundamental approach tosolve the moisturizing problem, there is, however, a further need forimprovement, for example in order to make it possible to exactly meterthe correct amounts of oxidant at the correct point, without having touse a complex control device for this purpose.

The object of the present invention is therefore to further develop afuel cell of the type described above such that the metering of fluidwith no or little moisturization, in particular oxidant, into therelevant fluid area can be further improved with regard to the profileof the relative moisture along the fluid area, in a simple manner. Afurther aim is to provide a corresponding separator plate unit.

The object is achieved by the features of the independent claims.Preferred embodiments are specified in the dependent claims.

The fuel cell according to the invention has a membrane electrodeassembly which is arranged between two separator plate units and, fordistribution of a first fluid, a first fluid area which is adjacent toone side of the membrane electrode assembly and, for distribution of asecond fluid, a second fluid area which is adjacent to a side of themembrane electrode assembly which is opposite this side, wherein aseparating wall is arranged in at least one fluid area and subdividesthe fluid area into at least one metering area and one fluid subarea,wherein the at least one metering area has a fluid connection to theadjacent fluid subarea at at least one metering point, such that thefirst fluid can be metered from the metering area through the meteringpoint into the adjacent fluid subarea. The fuel cell is distinguished inthat, starting from an edge inlet of the first fluid into the fluidarea, a cross section of the fluid subarea increases in the flowdirection of the first fluid towards an outlet of the fluid from thefluid area. The relative humidity, in particular the oxidant, of thefluid can thus be homogenized in a simple manner along its flow path.For the preferred case, in which the fluid area is a cathode area andthe fluid is an oxidant, this results in the advantage that only a smallamount of gas is available at the inlet area of the oxidant, and thisamount of gas preferably increases continuously along the flow directionto the outlet from the fluid area or cathode area. This makes itpossible to effectively prevent the membrane electrode assembly fromdrying out at the inlet area for the oxidant in the cathode area.

A cross section of the metering area can advantageously decrease in theopposite sense to the fluid subarea. This results, overall, in aseparator plate unit with a uniform thickness.

The cross section of the fluid subarea can be adjusted as a function ofa fluid requirement, in particular oxygen requirement, of the membraneelectrode assembly and/or as a function of a desired relative humidityof the fluid in the fluid subarea, to be precise of the oxidant in thecathode subarea. The relationships are preferably chosen such that, onthe one hand, sufficient oxygen for the fuel cell reaction is availableon the cathode side of the membrane electrode assembly while, on theother hand, the amount of oxidant is in each case sufficiently low thata high relative humidity is created quickly by the product water. Therelative humidity is expediently kept below the saturation limit in thiscase, at least in the area close to the metering points.

A corresponding configuration on the anode side, that is to say in theanode area of the fuel cell, is also feasible.

A simple geometry is obtained by arranging the separating wall inclinedwith respect to the membrane electrode assembly. The membrane electrodeassembly typically has a thin shape, in the form of a plate.

The separating wall may have a plurality of holes or bores along itslongitudinal extent, starting from the inlet port of the first fluid, inparticular of the oxidant, through which the oxidant enters the fluidarea, or cathode area, from the metering area.

The locations where the holes should advantageously be arranged alongthe longitudinal extent of the separating wall depends on the operatingparameters (pressure, temperature, moisture, stoichiometry, etc.). Itmay be the case, for example, that the holes should advantageously bearranged on approximately the first third of the longitudinal extent,for certain operating parameters. In different operating conditions(high temperature, low or no moisture, lower pressure), it may beadvantageous to arrange the holes along the entire longitudinal extent.However, in this case, it should be remembered that the effect of themetering at the end of the longitudinal extent is then only very minorsince a large gas volume is already present. Furthermore, it isadvantageous to increase the distances between the holes in thedirection from the inlet port to the outlet port. This results in thedistances between the holes being greater close to the outlet than closeto the inlet, thus further reducing the effect of the metering at theend of the longitudinal extent.

The separating wall may be in the form of a thin foil, which ispreferably metallic. The separating wall can be manufactured quickly andin large quantities and with large dimensions by means of simplestamping processes. This is particularly advantageous for large-scaleproduction processes for motor vehicle applications in which short cycletimes are normally desirable and large numbers of components must beproduced.

It is particularly advantageously possible to fill the cathode subarea,close to the cathode, with a porous material for gas distribution. Byway of example, the porous material may be a metal foam or a granulateor the like that is sintered together. These materials can be producedeasily and, furthermore, can easily be made into the required wedgeshape.

If the metering area is likewise filled with a porous material,identical parts can be used for the two areas. The wedges are simplyplaced on one another with their gradients in opposite directions, thenresulting in the desired rectangular block. The separating wall caneasily be located between them.

In this case, a metallic connection may be advantageous between theindividual parts and/or a specific surface coating of the individualparts, in order to reduce the electrical contact resistances.

The porosity of the material makes it possible to dispense with complexchannel structures in the separator plate units, which are otherwiserequired for gas transport of the fuel and of the oxidant. Channels suchas these are subject to very strict manufacturing tolerances, thusmeaning correspondingly expensive manufacture. Furthermore, the porousstructure allows a fine distribution of the contact surfaces for themembrane electrode assembly. This has been found to be advantageous forsupplying gas into the gas diffusion layer and for transporting wateraway from the gas diffusion layer. It may even be possible to reduce thethickness of the gas diffusion electrode. Since, in normal stacks,several hundred individual fuel cells are stacked one on top of theother, a reduction in the thickness of the individual components ishighly advantageous overall for the physical size of the stack. If thegas diffusion electrode thickness is reduced, there can be made morehydrophobic than when the thickness is greater, which in turn isadvantageous for an improved water hold-back capability for the membraneelectrode assembly. The embodiment is particularly advantageous when aseparating wall is provided in the cathode area and the anode area hasno separating wall but is filled with porous material.

The separator plate unit according to the invention is distinguished inthat, starting from an edge inlet port of the fluid into the fluid area,a cross section of the fluid subarea increases in the flow direction ofthe fluid towards an outlet port.

A cross section of the metering area advantageously decreases in theflow direction of the fluid. This results in the separator plate unithaving a constant thickness.

The fluid subarea can preferably be filled with a porous electricallyconductive material. This makes it possible to avoid a complex channelstructure with strict tolerances. Gas distribution advantageously takesplace through the porous material.

The metering area can advantageously also be filled with a porouselectrically conductive material.

The fluid area is preferably a cathode area, and the fluid is anoxidant. In addition, however, the anode area can also be formed in theindicated manner. It is advantageous if the anode area is at leastlikewise filled with a porous electrically conductive material, whichreplaces the channel structures of the distribution channels, even whenthere is no intention of providing a separating wall in the anode area.

The subject matters according to the invention can be used industriallyfor example in the field of generation of electric power for tractionand/or for power supply systems in vehicles.

The invention will be explained in more detail in the following text. Tothis end, the figures show specific exemplary embodiments of theinvention in a simplified form, and these will be explained in moredetail in the following description.

In the figures:

FIG. 1 shows, schematically, a single fuel cell with a membraneelectrode assembly, with a gas area of a separator plate unit beingadjacent to each of the two sides of the membrane electrode assembly;

FIG. 2 shows a preferred separator; and

FIG. 3 shows a profile of a relative humidity of an oxidant in its flowdirection in a fuel cell according to the invention.

Functionally identical elements are annotated with the same referencesymbols in the figures.

FIG. 1 shows a schematic illustration in the form of a section through asingle fuel cell 10. A multiplicity of such fuel cells 10 are stackedone on top of the other in conventional stacks, such as those which areused for traction or for power supply in vehicles, to form a stack inthe direction of the normal to the surfaces.

The fuel cell 10 has a membrane electrode assembly 16 in which in eachcase one gas diffusion electrode 20, 22 is adjacent to an ion-conductingpolymer membrane 18, on both sides. On the cathode side, adjacent to themembrane electrode assembly 16, a cathode area follows as the firstfluid area 12, with an oxidant as the first fluid, which is supplied tothe fluid area 12 via an inlet port 24, and is carried away again via anoutlet port 26. An anode area is formed as the second fluid area 14adjacent on the anode side, with a hydrogen-rich fuel as the secondfluid, which is supplied via an inlet port 28 and is carried away fromthe fluid area 14 via an outlet port 30. The fluid areas 12, 14 arecomponents of their respective separator plate units 44. The flowdirection of the second fluid (reduction agent) is indicated by arrowsto the left. The flow direction 40 of the oxidizing fluid (oxidant)which results from the position of the inlet port 24 and of the outletport 26 is indicated by arrows pointing to the right. The oxidant andreduction agent in this example flow in opposite directions past themembrane electrode assembly 16.

At this point, it should be mentioned that separator plate units 44,particularly when they are in the form of bipolar plates for a stackstructure, normally each have an anode plate and a cathode plate, whichare electrically conductively connected to one another. The electricallyconductive connection can be produced, for example, with the aid of ametal foil arranged between the anode plate and the cathode plate.

A separating wall 36 is arranged within the first fluid area 12, whichis in the form of a cathode area, and subdivides the fluid area 12 intoa metering area 32 remote from the cathode and a fluid subarea 34 closeto the cathode. The separating wall 36 is arranged inclined with respectto the membrane electrode assembly 16. The angle between the membraneelectrode assembly 16 and the separating wall 36 is preferably between5° and 80°. The thickness of the separating wall 36 for vehicleapplications is preferably in the range from 0.5 to 4 mm, and its widthis preferably in the range from 200 to 1000 mm. The separating wall 36is preferably in the form of a thin metallic foil.

The metering area 32 has a plurality of metering points 38 as a fluidicconnection to the adjacent fluid subarea 34 close to the cathode, suchthat the oxidant (first fluid) can be metered from the metering area 32through the metering points 38 into the adjacent fluid subarea 34, whichis in the form of a cathode subarea, as is indicated by small arrowsfrom the metering area 32 into the fluid subarea 34.

Starting from an inlet port 24 at the edge for the oxidant into thefluid area 12 which is in the form of a cathode area, the cross sectionof the cathode area 34 close to the cathode increases in the flowdirection 40 of the oxidant towards the outlet port 26, whereas thecross section of the metering area 32 decreases in the opposite sense tothe fluid area 34, which is in the form of the cathode area close to thecathode.

Overall, this therefore advantageously results in the cathode areaassociated with the separator plate unit 44 having a uniform thickness.In the situation in which the separator plate unit 44 does not have auniform thickness, it is advantageous to arrange two identical separatorplate units 44 in a stack such that this results in a uniform thicknessoverall for the arrangement.

The fluid area 12 is filled with a porous metallic material 46 whichreplaces the conventional gas distribution channels. The cross sectionof the fluid subarea 34 close to the cathode is preferably dependent onthe oxygen requirement of the membrane electrode assembly 16 and/or isdependent on the desired relative humidity of the oxidant in thecathode-side fluid area 34, which is in the form of the cathode subarea.The metering area 32 is also filled with the porous material 46. Themetering area 32 and the fluid subarea 34 close to the cathode are inthe form of wedges and are arranged in opposite senses to one another.

The second fluid area 14, which is in the form of an anode area, is notsubdivided by a separating wall but is advantageously likewise filledwith a porous material 46.

Along its longitudinal extent 42 starting from the inlet port 24 for theoxidant, the separating wall 36 has a plurality of metering points 38 inthe form of holes, as can be seen on the basis of a plan view of apreferred separating wall 36, in FIG. 2. A plurality of parallel rows ofmetering points 38 are arranged along the longitudinal extent 42 of theseparating wall, with the rows being formed at right angles to thelongitudinal extent 42.

In this example, the metering points 38 start close to the inlet and arearranged over about 75% of the longitudinal extent 42. No meteringpoints 38 are provided at the opposite end to the inlet port 24.

FIG. 3 shows the profile of the relative humidity φ (52, 52 a, 52 b)along a longitudinal extent L of a fluid area 12 in the form of acathode area in one preferred embodiment of the fuel cell 10 accordingto the invention.

In the illustrated case, the metering area 32 is designed such thatsaturation is reached with φ=1, but is not exceeded, at the meteringpoints 38, only one of which, annotated 38, is illustrated in arepresentative form, for the sake of clarity. For comparison, twobranches 52 a, 52 b of the profile of the relative humidity φ in thisarea are illustrated below the saturation point 50: the upper branch 52a has a sawtooth-like profile and merges into the profile 52 at thesaturation point 50. Together, the profiles 52 a and 52 form the profileof the relative humidity φ (52, 52 a) in a fuel cell 10 according to theinvention.

The lower branch 52 b, shows, for comparison with this, the profile ofthe relative humidity φ in this area in a conventional fuel cell. Thelower branch 52 b likewise merges into the profile 52 at the saturationpoint 50. The profiles 52 b and 52 together form the profile of therelative humidity φ (52, 52 b) in a conventional fuel cell.

The sawtooth-like profile of the upper branch 52 a of the relativehumidity φ (52, 52 a) in the fuel cell 10 according to the invention isexplained as follows: the unmoisturized oxidant, for example ambientair, enters the metering area 32 at the inlet port 24 with the inlethumidity φ_(E) at L=0 mm. However, according to the invention the entirevolume of the oxidant that is required for the fuel cell reaction doesnot enter there but only a small portion of it. The relative humidity φof the oxidant increases sharply in the flow direction 40 because of theproduct water which is created in the fuel cell reaction. The rise isparticularly sharp in comparison to conventional fuel cells because theamount of metered oxidant is less than in the case of conventional fuelcells, but approximately the same amount of product water is created, sothat the ratio of the partial pressures of water vapor to oxidant in thefuel cell 10 according to the invention is higher than in the case ofconventional fuel cells. The relative humidity φ then decreases abruptlyat the first metering point 38 in the flow direction 40, or at the firstrow of metering points 38, because relatively dry oxidant is added,which once again shifts the ratio of the partial pressures in favor ofthe oxidant. The relative humidity φ rises sharply from the start againafter this in the flow direction 40, until the oxidant is once againadded at the next row of metering points 38, etc., until the end of themetering points 38 of the metering area 32 is reached, for example wherethe saturation point 50 is reached.

This makes it possible to increase the relative humidity φ in the areaof the inlet of the oxidant into the fluid area 12, which is in the formof a cathode area, of a fuel cell 10 according to the invention incomparison to a conventional fuel cell, such that the risk of thepolymer membrane 18 drying out in this area is reduced or evenprevented. On the other hand, the metering area 32 in the fuel cell 10according to the invention is designed such that the relative humidity φdoes not exceed saturation, that is to say φ=1, anywhere. This canensure that no liquid water is created in the region of the meteringarea 32, which is provided with metering points 38, which liquid watercould, in poor circumstances, block the metering points 38. Overall, therelative humidity φ in the area of the inlet port 24 of the oxidant intothe fluid area 12, which is in the form of a cathode area, of a fuelcell 10 according to the invention can thus be increased in comparisonto a conventional fuel cell, but without any risk of droplet formationand blockage of the metering points 38.

1. A fuel cell having a membrane electrode assembly (16) which isarranged between two separator plate units (44), the separator plateunits having a first fluid area (12) for distribution of a first fluid,which is adjacent to a first side of the membrane electrode assembly(16), and having a second fluid area (14) for distribution of a secondfluid, which is adjacent to a second side of the membrane electrodeassembly (16) opposite the first side, wherein a separating wall (36) isarranged in at least one of said first and second fluid areas (12, 14)and subdivides the fluid area (12, 14) into at least one metering area(32) and one adjacent fluid subarea (34), wherein the at least onemetering area (32) has a fluid connection to the adjacent fluid subarea(34) at least one metering point (38), such that the first fluid can bemetered from the metering area (32) through the metering point (38) intothe adjacent fluid subarea (34), said first and second fluid areas (12,14) each having an edge inlet port (24) and an outlet port (26),wherein, starting from an edge inlet port (24) of the fluid into thefluid area (12), a cross section of the fluid subarea (34) increases inthe flow direction (40) of the first fluid towards an outlet port (26),and wherein the metering area (32) is filled with a porous material(46).
 2. The fuel cell as claimed in claim 1, wherein a cross section ofthe metering area (32) decreases in the flow direction (40) of the firstfluid.
 3. The fuel cell as claimed in claim 1, wherein the crosssections of the fluid subarea (34) and metering area (32) result overallin a separator plate unit (44) with a uniform thickness.
 4. The fuelcell as claimed in claim 1, wherein the cross section of the fluidsubarea (34) is adjusted on the cathode side to provide sufficientoxygen for the fuel cell reaction of the membrane electrode assembly(16) and/or to create a high relative humidity of the fluid in the fluidsubarea (34).
 5. The fuel cell as claimed in claim 1, wherein theseparating wall (36) has a plurality of metering points (38) along itslongitudinal extent (42) starting from the inlet port (24) of the firstfluid.
 6. The fuel cell as claimed in claim 1, wherein the separatingwall (36) is metallic.
 7. The fuel cell as claimed in claim 1, whereinthe fluid subarea (34) is filled with a porous material (46) for gasdistribution.
 8. The fuel cell as claimed in claim 7, wherein the porousmaterial (46) is metallic.
 9. The fuel cell as claimed in claim 1,wherein the fluid area (12) is provided as a cathode area.
 10. Aseparator plate unit of a fuel cell (10) having a cathode area and/or ananode area as a first and a second fluid area (12, 14) for distributionof a first and a second fluid, which are adjacent to a membraneelectrode assembly (16), wherein a separating wall (36) is arranged inat least one of the fluid areas (12, 14) and subdivides the at least onefluid area (12, 14) into at least one metering area (32) and oneadjacent fluid subarea (34), and wherein the at least one metering area(32) has a fluidic connection to the adjacent fluid subarea (34) atleast one metering point (38), such that a first fluid can be meteredfrom the metering area (32) through the metering point (38) into theadjacent fluid subarea (34), wherein, starting from an edge inlet port(24) of the first fluid into the fluid area (12), a cross section of thefluid subarea (34) increases in the flow direction (40) of the firstfluid towards an outlet port (26), and wherein the metering area (32) isfilled with a porous electrically conductive material (46).
 11. Theseparator plate unit as claimed in claim 10, wherein a cross section ofthe metering area (32) decreases in the flow direction (40) of the firstfluid.
 12. The separator plate unit as claimed in claim 10, wherein thefluid subarea (34) is filled with a porous electrically conductivematerial (46).
 13. The separator plate unit as claimed in claim 10,wherein the fluid area (12) is a cathode area.